1. Technical Field
The invention relates to an illumination device for use in an endoscope.
2. Description of the Related Art
In light source devices using a laser beam, various types of light source devices which obtain white light by a laser beam and visible light generated by a wavelength conversion member, such as a phosphor excited by the laser beam, have been proposed. In these types of light source devices, a laser beam has a line spectrum in a specific wavelength region. Accordingly, a wavelength region where the emission intensity is low may be generated over a relatively wide range around the wavelength region of the line spectrum. For this reason, in normal illumination, a phosphor which emits light in a broad wavelength region is appropriately selected in order to improve the color rendering properties. Moreover, the wavelength region where the emission intensity is low may be compensated by adding other kinds of laser beams in addition to the above laser beam. For example, JP 2006-173324 A (corresponding to US 2006/0152926 A and US 2008/0205477 A) describes an example where a blue laser beam as excitation light and a laser beam having a different excitation wavelength from the blue laser beam are added.
Meanwhile, in a light source device for use in the endoscope filed, illumination light for diagnosis under light in a specific wavelength band may be required in addition to obtaining white light having high color rendering properties. In a technique called a spectral diagnostics in the endoscope filed, a new blood vessel, which is generated in a mucous membrane layer or an underlying layer of a mucous membrane, is observed using the light in the specific wavelength band so as to determine if there is cancer. Illumination light used for observation has a larger scattering characteristic as the wavelength becomes short. Therefore, information about a relatively shallow layer can be obtained with a short wavelength, and information about a relatively deep layer can be obtained with a long wavelength. For this reason, in case of observing the surface microstructure while a deep reaching degree of light is limited to a surface layer, it is important to make a band of illumination light narrow in order to improve the contrast. For example, JP Hei.6-40174 A describes an endoscope for performing an illumination operation with light which is in a narrow wavelength band and which is extracted by using a narrow-band filter.
Moreover, for endoscopic diagnosis of an upper alimentary canal, a nasal endoscope less stressful to a patient is being used in place of a peroral endoscope. In the case of the nasal endoscope, an insertion portion is thinner than that of the peroral endoscope, and it is difficult to secure the thickness of a light guide. Accordingly, in order to capture a bright image, improvements are required such as increasing an amount of illumination light or improving a sensitivity of an imaging device.
Furthermore, also in the thin endoscope, measurement and diagnosis in a narrow band are beginning to be required. Narrow-band diagnosis is disclosed in “Trials for development and clinical application of an electronic endoscope system having a built-in narrow band filter (Narrow Band Imaging: NBI)” (Yasushi Sano, Shigeaki Yoshida (National Cancer Center East Hospital), Masahiko Kobayashi (Self-Defense Forces Central Hospital), GastroenterolEndosc, Sep. 20, 2000.).
Also, JP 2641653 B2 describes an electronic endoscope capable of selecting an optimal wavelength region according to an observed body and acquiring a normal color image (visible information) with time-series illumination within a visible wavelength band using a solid state imaging device provided in the tip portion of the endoscope. The electronic endoscope of this reference is also capable of acquiring an image with infrared light or ultraviolet light by illuminating such light, which includes an infrared or ultraviolet wavelength band other than the visible wavelength band, in a time-series manner in order to easily detect a color tone difference of each part of the observed body, which is difficult to be distinguished in a normal image in the visible region, and displaying the image with desired colors assigned. Therefore, JP 2641653 B2 describes that a laser or an LED which emits light in a narrow wavelength region is exemplified as a light source for performing illumination using light in the narrow wavelength region. Also, JP 2641653 B2 describes that a light source being provided with an absorption type filter in which coloring materials are mixed or a vapor-deposited type filter on an emission port of a lamp which emits light in a wide band, such as a xenon lamp, a halogen lamp, and a strobe lamp in order to limit an output wavelength may also be used. Moreover, JP 2641653 B2 describes that a plurality of such light sources are used in a wavelength region from an ultraviolet region to an infrared region. In addition, since various kinds of illumination light in a predetermined wavelength region from an ultraviolet region to an infrared region need to be guided in JP 2641653 B2, it describes that illumination light emitted from the light source is guided to the tip of the endoscope by a light guide similar as in the related art.
Thus, the endoscope for use in spectral diagnostics is requested to emit narrow-band light while making it compact. In a light source described in JP 2006-173324 A, in order to obtain emission of green light having a narrow bandwidth, coupling using a so-called DPSS green SHG laser by second harmonic generation is performed on the light source side, for example, by using a prism. However, in this method, it is requested that a phosphor, which is excited by a blue laser beam to emit light of green to red colors do not absorb, for example, green light introduced by other laser beams. That is, as a phosphor disposed in the middle of an optical path in order to acquire white light, there is no choice but to apply only a phosphor which rarely absorbs a laser beam for obtaining light in a specific wavelength band other than a laser beam for generation of white light. Moreover, in case of performing illumination with such a green laser, a noise is easily superimposed on a captured image because of speckle (interference) or flickering easily occurs on a dynamic image due to the high coherence. Moreover, it may be conceived to eliminate the limitation of a phosphor by providing a white light illumination optical system and an illumination optical system of a specific wavelength band as separate optical paths. However, particularly in an endoscope, a light guide serving as an optical path becomes bulky. In addition, since it is necessary to provide a new irradiation window at the tip of an insertion portion, it becomes difficult to make the insertion portion thin. Moreover, the light source described in JP 2006-173324 A irradiates light in a visible wavelength region like JP Hei.6-40174 A or the non-patent document ('Trials for development and clinical application of an electronic endoscope system with a built-in narrow band filter (Narrow Band Imaging: NBI)'). Accordingly, in order to improve the color rendering properties, the wavelength width of emitted light is made wide. Therefore, in order to acquire a narrow-band imaging signal of a blue or green color which is useful especially for an endoscope, there still remains many problems in a combination of suitable phosphors, switching of excitation light sources in a time-series manner, a signal calculating method, and the like. That is, it is still difficult to precisely separate the emission wavelength band by switching of excitation light and to make light selectively emitted.
In the case of mounting a light emitting device, such as an LED or a semiconductor laser, in a tip portion of the endoscope, particularly in the case of disposing a plurality of light emitting devices as described in JP Sh.60-225820 A, it is requested to make the light emitting devices very small and thin. Thus, in the case of white illumination suitable for illumination of an endoscope, for example, in the case of using a white LED or a white laser, the illumination system may be configured by a semiconductor laser or an LED used as an excitation light source and a phosphor as described in JP 2005-205195 A and JP 2006-173324A. In this case, however, trade-offs between making the phosphor very large and improving the efficiency occur. For this reason, since there was limitation in the size of a phosphor when a light emitting device is mounted at the tip portion of the endoscope, there was also limitation in improving the efficiency.
On the other hand, infrared light and ultraviolet light other than a visible range may also be used to acquire a useful image for diagnostic imaging, especially medical image diagnosis like the endoscope described in JP 2641653 B2. However, the endoscope apparatus described in JP 2641653 B2 is an apparatus in which both light in a visible range and infrared light or ultraviolet light other than the visible range are used by switching light having a narrow-band wavelength in a time-series manner, and such light components are directly incident on a light guide to be then directly irradiated to a body to be inspected from the tip of the light guide, but is not an apparatus that irradiates white light including plural wavelength components in a visible range. Therefore, JP 2641653 B2 describes that a fiberscope which uses an optical fiber may be used instead of the electronic endoscope which uses a light guide. However, in the technique described in JP 2641653 B2, the optical fiber is used only to guide light having many narrow-band wavelengths like a light guide. Accordingly, in the endoscope described in JP 2641653 B2, even if an optical fiber is used in place of the light guide, it was not possible to use a white LED and a white laser, which are described in JP 2005-205195 A and JP 2006-173324 A in which white light is obtained by making light emitted from a semiconductor laser or an LED serving as an excitation light source incident on a light guide or an optical fiber and by coating the tip of the light guide or the optical fiber with a phosphor.
Moreover, it is assumed that as a light source of an endoscope, used is a white LED or a white laser including: a semiconductor laser or an LED which emit excitation light, for example, blue excitation light; an optical fiber which guides the excitation light; and a phosphor provided at the tip of an optical fiber and excited by excitation light as described in JP 2005-205195 A and JP 2006-173324 A and that an infrared emitting device which is useful in medical fields and emits infrared light other than a visible range like the endoscope described in JP 2641653 B2. In this case, the infrared light could not be efficiently guided in the related art because the optical fiber which guides the excitation light is configured to efficiently guide the excitation light. In addition, in the case of a phosphor for use in the known white LED or white laser, there was a problem that the infrared light was wavelength-converted into fluorescent light.
For this reason, in a light source device of the related art for an endoscope, excitation light and infrared light are guided using separate optical fibers. An endoscope apparatus using such a light source device for an endoscope is shown in FIG. 32. As shown in FIG. 32, an endoscope apparatus 400 has an endoscope device 402 and a control device 404. The endoscope device 402 is configured to include an insertion portion 406, an operating section 408, a main body operating section 410, and a connection portion 412. The insertion portion 406 is configured to have a flexible soft portion 414, a bending portion 416, and a tip portion 418. A phosphor portion 420, an irradiation port 422 for illumination light, an objective lens (not shown), and a CCD 424 are provided in the tip portion 418 of the insertion portion 406. Moreover, the control device 404 includes a blue laser diode (hereinafter, referred to as an LD) 426 and an infrared LD 428, which serve as light sources of excitation light, a light source controller 430 that controls the blue LD 426 and the infrared LD 428 to emit light in a time-series manner, and a processor 432.
In addition, two optical fibers 434 and 436 and one scope cable 438 are inserted inside the endoscope device 402. The optical fibers 434 and 436 are inserted in the endoscope device 402. One ends of the optical fibers 434 and 436 are connected to the blue LD 426 and the infrared LD 428 of the control device 404, respectively, and the other ends extend to the tip portion 418 of the endoscope device 402. In the tip portion 418 of the endoscope device 402, the tip of the optical fiber 434 extends to the position of the phosphor portion 420 so that blue light from the blue LD 426 is incident on the phosphor portion 420 and is then emitted from the irradiation port 422 as white light (or pseudo white light) that becomes illumination light. The tip of the optical fiber 436 extends to the irradiation port 422 so that infrared light from the infrared LD 428 is emitted from the irradiation port 422. In addition, the scope cable 438 is a cable for transmission of an imaging signal. One end of the scope cable 438 is connected to the processor 430 of the control device 404, and the other end is connected to the CCD 424. The processor 430 converts the imaging signal transmitted from the CCD 424 into a video signal and supplies the video signal to a monitor (not shown).
Here, the blue LD 426, the infrared LD 428, the two optical fibers 434 and 436, and the phosphor portion 420 form a light source device 440. Details of the light source device 440 are shown in FIG. 33. As shown in FIG. 33, a collimator lens 442 is disposed between the blue LD 426 and the optical fiber 434, and an illumination optical member 446 to which the phosphor portion 420 is attached is provided at the tip of the optical fiber 434, which is held by a holding end portion 444. In addition, a collimator lens 448 is disposed between the infrared LD 428 and the optical fiber 436, and a concave lens 450 is provided at the tip of the optical fiber 436. In the light source device 440 of the related art, infrared light from the infrared LD 428 is independently guided by the optical fiber 436. Therefore, the concave lens 450 is needed at the tip of the optical fiber in order to increase the divergence angle of the infrared light.
In the case where, like this light source device 440, a white laser configured to include the blue LD 426, the optical fiber 434, and the phosphor portion 420 are used as an observation light source, if the infrared LD 428 is used together as an observation light source for making observation under the infrared light that is effective in the medical field, the dedicated optical fiber 436 which guides the infrared light and is different from the optical fiber 434 guiding blue excitation light from the blue LD 426 needs to be used. However, the resultant device configuration is complicated, and it is difficult to reduce a size of the device. In addition, emission positions of white light and infrared light are not identical. Therefore, for example, when normal images under the white light and images under the infrared light are acquired in a time-series manner and displayed, a difference between images and/or appearance of a shadow would be conspicuous. Therefore, it is difficult to compare the images.
Moreover, in the case where an infrared emission LED device is used to make observation under infrared light that is effective in the medical field, even if a white (or pseudo white) LED formed of a blue LED device and a phosphor and an infrared emission LED device are integrated as a light source device for an endoscope, it is necessary to seal the white LED and the infrared emission LED device. Such a light source device for an endoscope is shown in FIG. 34. As shown in FIG. 34, a light source device 460 includes: a common substrate 464 formed with two recesses 462 and 463 separated by a separation barrier 461; a blue LED device 468 fixed to the recess 462 by an adhesive 466; a resin sealing portion 470, which seals the blue LED device 468 provided in the recess 462, in a sealing region with a phosphor-containing resin in which a phosphor is mixed; an infrared emission LED device 472 fixed to the recess 463 of the common substrate 464 by an adhesive; and a resin sealing portion 474, which seals the infrared emission LED device 472 provided in the recess 463, in a sealing region with a resin in which a phosphor is not mixed, the resin sealing portion 474 which allows infrared light to transmit therethrough. Here, the blue LED device 468 and the resin sealing portion 470 formed of the phosphor-containing resin form a white (or pseudo white) LED, and white light (or pseudo white light) is emitted from the resin sealing portion 470. In addition, the infrared emission LED device 472 emits infrared light through the resin sealing portion 474.
In the case where, like this light source device 460, a white LED including the blue LED device 468 and the resin sealing portion 470 formed of the phosphor-containing resin is used as an observation light source, if the infrared LED 472 is used together as an observation light source for making observation under the infrared light that is effective in the medical field, it is necessary to use a resin in which a phosphor is not mixed for sealing the infrared LED 472, while it is necessary to mix the phosphor, which is excited by blue excitation light from the blue LED device 468 and converts wavelength into white light (or pseudo white light), in a resin for sealing the blue LED device 468, while a resin in which a phosphor is not mixed needs to be used as a resin for sealing the infrared emission LED device 472. Therefore, it would be difficult to achieve efficient white illumination and to reduce a size of the device. In addition, since emission sources of white light and infrared light are not identical, for example, when normal images under the white light and images under the infrared light are acquired in a time-series manner and displayed, a difference between images and/or a difference in appearance of shadows are conspicuous. Therefore, it is difficult to compare both the images.